Heteroleptic complexes: Via solubility control: Examples of Cu(ii), Co(ii), Ni(ii) and Mn(ii) complexes based on the derivatives of terpyridine and hydroxyquinoline

Article abstract of DOI:10.1039/c7dt03387g

We describe the construction of synthetically challenging heteroleptic complexes by capitalizing on the solubility properties of their corresponding favored homoleptic complexes. We demonstrate that the formation of a heteroleptic Cu²⁺ complex based on 2,2′:6′,2′′-terpyridine (Terpy) and 8-hydroxyquinoline (HQ) is not possible due to the insolubility of (HQ)₂Cu²⁺. Replacing HQ with 8-hydroxy-2-quinolinecarbonitrile (HQCN) enabled the solubility of (HQCN)₂Cu²⁺ in acetonitrile, leading to the formation of the heteroleptic complex Terpy(HQCN)Cu²⁺, TQCu. Applying these conditions to the synthesis of the corresponding heteroleptic Co²⁺ complex resulted in TerpyCo²⁺(acetate)₂, which is insoluble in acetonitrile. Upon changing the solvent to methanol, the carbonitrile group of HQCN was converted to carboxyimidate HQOMe yielding a heteroleptic complex Terpy(HQOMe)Co²⁺, TQ′Co. Using this method, we also generated the heteroleptic complex TQ′Ni and the polynuclear heteroleptic complex Q′₄Q′′₂Mn₄ (Q′′ = HQO₂Me). Detailed analysis of the complexes included characterization by X-ray diffraction, EPR, UV-Vis, high resolution ESI MS, DFT calculations and electrochemistry. X-ray analysis of TQCu revealed distorted square pyramidal geometry, while TQ′Co and TQ′Ni exhibit distorted octahedral geometry, which includes metal coordination via the carboxyimidate nitrogen site. Interestingly, Q′₄Q′′₂Mn₄ was found to contain a [MnII4(μ₃-O)₂(μ₂-O)₄N₁₀]²⁺ core, which adopts a distorted octahedral geometry, and two types of HQ chelators. Thus, Q′₄Q′′₂Mn₄ is also heteroleptic even though it does not contain a Terpy ligand. Solution studies revealed that while TQCu is stable in solution, TQ′Co and TQ′Ni go through ligand exchange and are partially converted to their corresponding homoleptic complexes. Based on these data we could propose a mechanism for the formation of TQ′Co and TQ′Ni and show that TQ′Co can be prepared directly from Terpy and HQOMe.

Full text of DOI:10.1039/c7dt03387g

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Heteroleptic Complexes via Solubility Control:
Examples of Cu(II), Co(II), Ni(II) and Mn(II)
complexes Based on the Derivatives of Terpyridine
and Hydroxyquinoline
Maria Baskin, Natalia Fridman, Monica Kosa and Galia Maayan*
Schulich Faculty of Chemistry, TechnionꢀIsrael Institute of Technology, Haifa, 32000, Israel.
Abstract
We describe the construction of synthetically challenging heteroleptic complexes by capitalizing
on the solubility properties of their corresponding favored homoleptic complexes. We
demonstrate that the formation of a heteroleptic Cu2+ complex based on 2,2’:6’,2’’ꢀterpyridine
(Terpy) and 8ꢀhydroxyquinoline (HQ) is not possible due to the insolubility of (HQ)2Cu2+.
Replacing HQ with 8ꢀhydroxyꢀ2ꢀquinolinecarbonitrile (HQCN) enabled the solubility of
(HQCN)2Cu2+ in acetonitrile, leading to the formation of the heteroleptic complex
Terpy(HQCN)Cu2+, TQCu. Applying these conditions to the synthesis of the corresponding
heteroleptic Co2+ complex resulted in TerpyCo2+(acetate)2, which is insoluble in acetonitrile.
Upon changing the solvent to methanol, the carbonitrile group of HQCN was converted to the
carboxyimidate HQOMe yielding the heteroleptic complex Terpy(HQOMe)Cu2+, TQ’Co. Using
this method, we also generated the heteroleptic complex TQ’Ni and the polynuclear heteroleptic
complex Q’4Q’’2Mn4 (Q’’= HQO2Me). Detailed analysis of the complexes included
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characterization by Xꢀray diffraction, EPR, UVꢀVis, High Resolution ESI MS, DFT calculations
and electrochemistry. Xꢀray analysis of TQCu revealed distorted square pyramidal geometry,
while TQ’Co and TQ’Ni exhibit distorted octahedral geometry, which includes metal
coordination via the carboxyimidate nitrogen site. Interestingly, Q’4Q’’2Mn4 was found to
II
contain a [Mn4 (µ3ꢀO)2(µ2ꢀO)4N10]2+ core, which adopts a distorted octahedral geometry, and
two types of HQ chelators. Thus, Q’4Q’’2Mn4 is also heteroleptic even though it does not contain
a Terpy ligand. Solution studies revealed that while TQCu is stable in solution, TQ’Co and
TQ’Ni go through ligand exchange and are partially converted to their corresponding homoleptic
complexes. Based on this data we could propose a mechanism for the formation of TQ’Co and
TQ’Ni and show that TQ’Co can be prepared directly from Terpy and HQOMe.
Introduction
The ability to control the coordination environment about a metal ion has significant importance
in the design and development of metalꢀbased materials including catalysts, selective chelators,
sensors and biomimetic models. Typically, a coordination environment comprises metalꢀbinding
ligands (MBLs), which can be identical, thus creating homoleptic complexes, or varied, creating
heteroleptic complexes. The major advantage of heteroleptic complexes is the possibility to tune
and combine ligand structural and functional properties, thus increasing the versatility of the
metallic center.1 From the metallosupramolecular chemistry point of view, heteroleptic
complexes are in particular interest as they represent a promising research platform for the
construction of diverse and functional systems.2 Although such complexes have many
advantages, the majority of the known coordination complexes are homoleptic, which are highly
uniform and suffer from the lack of chemical and structural diversity.3 This is mostly because
2

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directing the exclusive generation of a heteroleptic product over the two corresponding
homoleptic complexes is highly challenging.4 In order to control the formation of heteroleptic
complexes in solution, several strategies can be implied as reported in the literature.5,3b One of
these strategies is based on maximum site occupancy6 and a use of sterically hindered MBLs,
which cannot form a bishomoleptic complexes due to steric repulsion. Thus, only a 1:1 L:M
complex is formed, and this further reacts with another ligand, which is less sterically hindered,
to form the desired heteroleptic complex. An example for this approach is the HETPHEN
strategy (HETeroleptic PHENanthroline) first applied by Schmittel and coworkers.7 Another
technique is the combination between shape complementary ligands, and this was applied, using
isoquinoline/pyridine ligands, to form heteroleptic [Pd2L2L’2]4+ coordination cages.8 A different
approach of constructing heteroleptic architectures is based on the properties of the metal ion
rather on these of the ligands and exploits the particular pentaꢀcoordination geometric preference
of copper(II) ions.9 Using this strategy, we have recently developed a rationally designed helical
peptidomimetic oligomer (peptoid) bearing two distinct MBLs, namely derivatives of 2,2':6',2''ꢀ
Terpyridine (Terpy) and 8ꢀhydroxyquinoline (HQ). This peptoid enabled the selective
recognition of Cu2+ and its extraction from a mixture of neighboring metal ions in high
concentrations by forming a heteroleptic copper center, as suggested by mass spectrometry and
UVꢀVis spectroscopy (Scheme 1).10 Moreover, EPR studies suggested a pentaꢀcoordination with
square pyramidal geometry. Hence, we hypothesized that this specific 3D arrangement is the
source of the high selectivity to Cu2+ over other similar biologically relevant metal ions11 such as
Zn2+, Fe3+, Co2+, Ni2+ and Mn2+ capable of binding these ligands.12 In order to examine this
assumption we set up to synthesize heteroleptic complexes based on Terpy, HQ and some of
these metal ions, investigate their properties, and compare their structures.
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Scheme 1 The helical peptoid Helix HQT i+3 bearing HQ and Terpy (left) rationally designed
for the selective binding of Cu2+, and its intramolecular Cu2+ complex (Helix HQT i+3)Cu
(right).
Results and Discussion
Attempts towards the synthesis of a heteroleptic copper complex. Our initial efforts to
synthesize the heteroleptic Terpy(HQ)Cu2+ complex included the reaction between the equimolar
mixture of the ligands HQ and Terpy with 1 equiv. of copper acetate in methanol (the mix
approach). This reaction resulted in an immediate precipitation of a dark green complex and a
bright blue solution. Further investigation of the precipitant and the solution by UVꢀVis analysis
revealed the formation of the homoleptic complex HQ2Cu that precipitate and Terpy2Cu
complex that remained in the solution (Fig. S1). Following this unsuccessful attempt we turned
our efforts to the synthesis of this complex via the step approach, which included (i) a slow
addition of equimolar ligands mixture solution to the Cu2+ solution, both in methanol, (ii)
addition of 1 equiv. of Terpy to 1 equiv. of Cu2+ in methanol followed by slow addition of 1
equiv. of HQ and (iii) addition of 1 equiv. of Cu2+ in methanol to the equimolar ligands mixture
solution. In addition, we used different copper salts such as copper perchlorate or copper triflate,
changed the solvent of the reaction to acetonitrile or increased the temperature of the solution to
50°C, even for a long period of time of up to 7 days. All these attempts, however, did not afford
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the heteroleptic complex, but rather yielded the homoleptic complexes as indicated by the
precipitation of HQ2Cu during each reaction. We assume that these unsuccessful attempts were
due to the poor solubility of the complex HQ2Cu both in methanol and acetonitrile and its
immediate precipitation, which shifted the reaction equilibrium towards its formation. Thus, we
sought to increase the solubility of the homoleptic complexes in order to avoid this problem and
chose to use a modified version of HQ ligand, namely 8ꢀhydroxyꢀ2ꢀquinolinecarbonitrile
(HQCN), assuming that the carbonitrile group will facilitate the complex solubility in acetonitrile
and enable the formation of the heteroleptic complex (Scheme 2). To verify this assumption, we
added 1 equiv. from each ligand to half an equiv. of Cu(II)triflate in 5 mL of acetonitrile. The
two solutions were mixed for 2 hours at 50°C. The precipitate of each solution was separated by
centrifugation, washed, dried and weighted, yielding 20.7 mg HQ2Cu and 1.3 mg (HQCN)2Cu.
Thus we have confirmed that (HQCN)2Cu is much soluble than HQ2Cu. Indeed, addition of an
equimolar mixture of Terpy and HQCN to a solution of Cu2+ triflate in acetonitrile and heating
the solution at 50ºC for 2 hours resulted in a dark green solution and no precipitation was
obtained. After addition of an aqueous solution of NH4PF6 a mustardꢀbrown complex was
precipitated. It was collected by decantation, washed with water, dried and characterized by
electrospray mass spectrometry (ESI MS) and UVꢀVis spectroscopy. The molecular weight of
the complex as measured by HRꢀESI MS was consistent with the expected mass of the
Terpy(HQCN)Cu2+ (TQCu) complex (Fig. S18ꢀ19), providing the first evidence for its
formation. UVꢀVis analysis of the complex in methanol supported the existence of TQCu in
solution, showing absorption bands near λ = 266, 325 and 338 nm arising from the coordination
of Cu2+ to both HQ and Terpy (Fig. S3). The complex was obtained in a moderate isolated yield
of about 60%, and we assume that due to its high solubility in acetonitrile, not all the complex
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actually precipitated and some of it remained in the solution. To support this assumption we have
analyzed the filtrate solution, after precipitation, by ESIꢀMS and the obtained spectra matched
the mass of TQCu (Fig. S27). We therefore believe that the actual yield of TQCu from this
reaction is higher than the isolated yield. Moreover, the ESIꢀMS spectra did not show any peaks
corresponding to the homoleptic complexes Terpy2Cu and Q2Cu (which can result from a ligand
exchange), suggesting that TQCu is stable in these conditions.
Scheme 2 Synthetic routs towards the generation of the heteroleptic complex TQCu.
Single crystals suitable for Xꢀray diffraction analysis were obtained by slow evaporation from
acetonitrile/THF solution at room temperature. The complex was crystallized in the monoclinic
crystal system (Fig. 1), have an open coordination site and exhibits slightly distorted square
pyramidal geometry with τ=0.188, which is an index of the degree of trigonality in five
coordinate complexes.13 The crystal structure confirmed the formation of TQCu.
Fig. 1 Xꢀray structure of TQCu complex. Color code: C, gray; N, blue; O, red; Cu, green.
Hydrogen atoms omitted for clarity. Ellipsoids are drawn at 50% probability level.
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EPR measurements conducted in frozen acetonitrile at 150K indicated the presence of Cu2+, and
the Hamiltonian parameters obtained from the simulation were g|| = 2.21, g⊥ = 2.063 and A|| =
170 G (Fig. 2). This values are in agreement with a square pyramidal coordination geometry14
and are similar to the values obtained for the complex (Helix HQT i+3)Cu from our previous
research (see scheme 1), which were g|| = 2.23, g⊥ = 2.070 and A|| = 175 G, indicating that
(Helix HQT i+3)Cu has a similar geometric structure, as we previously suggested.10
Fig. 2 Xꢀband EPR spectra of TQCu complex (blue line) and its corresponding simulated
spectra (red line). The measurements were performed in frozen acetonitrile solution at 150K,
with (2,2,6,6ꢀTetramethylpiperidinꢀ1ꢀyl)oxyl radical (TEMPO) as a reference (g = 2.0058).
Synthesis and characterization of heteroleptic cobalt and nickel complexes. In order to
show that our method can be generalized by applying it to other metal ions, we set to synthesize
the heteroleptic Co complex TQCo. Attempts to follow the synthetic procedure used for the
generation of TQCu were not successful; the obtained complex was the
mono(terpyridine)cobalt(II)bis(acetate), TCo, as indicated by its single crystal Xꢀray analysis
(Fig. S43). As this complex was not soluble in acetonitrile and precipitated from the reaction
solution, we again assumed that enabling its solubility by modifying the reaction conditions will
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lead to the formation of the heteroleptic complex as occurred in the case of Cu2+. Indeed,
applying the same reaction conditions in methanol instead of in acetonitrile yielded a dark red
powder, which was further analyzed. This complex exhibits absorption bands near λ = 280, 319
nm which corresponds to metal coordination of both HQ and Terpy respectively (Fig. S4). The
molecular weight of the complex as shown by HRꢀESIꢀMS suggested that the complex is bound
to methanol (Fig. S20ꢀ21). The complex is poorly soluble in MeOH, therefore single crystals
suitable for Xꢀray analysis were obtained by vapor diffusion of diethyl ether into an acetonitrile
solution of the complex. According to the Xꢀray structure, the complex crystallized in the
triclinic crystal system, having distorted octahedral structure with oneꢀcoordinated oxygen atom
and five coordinated nitrogen atoms (Fig. 3A). The Xꢀray structure revealed that one of the
coordinated nitrogen atoms is of an imidate group rather than of a carbonitrile group. This
observation suggests that the carbonitrile group reacted with methanol in a methanolysis
reaction, which was probably promoted by the metal and transformed into a carboxyimidate
group.15 Indeed, the molecular weight of the complex was consistent with this structure, showing
an addition of 32 mass units corresponding to the formation of carboxyimidate. This unique
example emphasizes the coordination requirements of the cobalt ion to form a hexaꢀcoordinated
complex and its inability to produce a stable pentaꢀcoordinated complex. Thus, a heteroleptic
Co2+ complex TQ’Co could be only obtained by the use of a solvent that not only coordinates as
a sixth (labile) ligand but actually reacts with one of the ligands resulting a modified ligand that
is able to strongly coordinate and stabilize this complex. To support this statement, the
intramolecular coordination in the Co2+ complex was studied using static calculations within
DFT. Based on these calculations, the five coordinated Co2+ complex is energetically unstable
and the addition of methanol to this complex following the coordination of the imine group to the
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Co2+ ion is highly exothermic with TQ’Co being 33.43 kcal/mol lower in enthalpy and 19.48
kcal/mol lower in free energy than the fiveꢀcoordinated complex in methanol (see SI for details).
Following this synthetic procedure, we next tried to synthesize the corresponding Ni2+
complex. Addition of an equimolar amount of the ligands to the solution of nickel acetate in
methanol and heating the solution at 50ºC for 2 hours following by precipitation with aqueous
NH4PF6 afforded orange powder. UVꢀVis analysis of the complex in methanol revealed
absorption bands near λ = 279, 320 and 334 nm, supporting the presence of both Terpy and HQ
ligands in the complex (Fig. S6). HRꢀESIꢀMS analysis of this complex indicated the addition of
32 units to the expected mass, which suggests either coordination to methanol or to a
carboxyimidate group similar to TQ’Co complex (Fig. S23ꢀ24). TQ’Ni complex is poorly
soluble in methanol, thus, it was reꢀdissolved in acetonitrile and crystalized by vapor diffusion of
diethyl ether. The Xꢀray structure of this complex is indeed very similar to its Co2+ analogue; it
has a triclinic crystal system with a distorted octahedral geometry and coordinates to the nitrogen
of a carboxyimidate that is formed by methanolysis of carbonitrile (Fig. 3B).
Fig. 3 Xꢀray structure of (A) TQ’Co and (B) TQ’Ni complexes. Color code: C, gray; N, blue; O,
red; Co, orange; Ni, turquoise. Hydrogen atoms omitted for clarity. Ellipsoids are drawn at 50%
probability level.
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Both TQ’Co and TQ’Ni were obtained in high isolated yield of about 90%. Here, the low
solubility of both complexes in methanol facilitated their precipitation such that their isolated
yields resemble their actual yields. The ESIꢀMS analysis of the complexes was further conducted
in acetonitrile due to their high solubility in this solvent. The ESIꢀMS spectra of both complexes
exhibited small peaks that correspond to the half masses of the homoleptic complexes Terpy2Co
and Terpy2Ni, Fig. S20 and S23, respectively, suggesting that some ligand exchange occurs
already at room temperature. In order to further investigate whether TQ’Co and TQ’Ni are
stable in solution or present in equilibrium along with the homoleptic complexes, we performed
ESIꢀMS and UVꢀVis analysis after 8 and 24 hours heating of their acetonitrile solutions at 80°C.
Upon heating, the UVꢀVis analysis of TQ’Co revealed small changes in the spectrum; after 24
hours of heating the peak of the modified HQ ligand was 5 nm blue shifted and the shape of the
Terpy peak was changed (Fig. S14). In the MS spectrum we noted the appearance of two peaks,
one at 262, which corresponds to m/2z of Terpy2Co and one at 461, corresponding to Q’2Co,
which their intensity was increased after 8 and 24 hours (Fig. S32ꢀ33). Both MS and UV analysis
suggest that the complex TQ’Co is not kinetically inert, as heating at 80°C for several hours lead
to ligand exchange as evident from the present of both the homoleptic and heteroleptic
complexes. Although the UVꢀVis spectrum of the TQ’Ni did not exhibit significant changes
(Fig. S15), we could observe the homoleptic complexes in the MS spectra (Fig. S35ꢀ36),
suggesting that TQ’Ni is also not kinetically stable. Therefore, we suggest that the heteroleptic
complexes TQ’Co and TQ’Ni exist in the solution in equilibrium with their corresponding
homoleptic Terpy complexes.
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Scheme 3 Proposed mechanism for the formation of heteroleptic TQ’M complexes.
On the basis of all the new data we have acquired, we can propose the following mechanism
for the formation of the heteronuclear complexes (Scheme 3): first, in methanol, M(OAc)2 (M =
Co2+ or Ni2+) gets bound either to Terpy, stabilized as a hexaꢀcoordinated complex by
coordination to three oxygen atoms from two acetate ligands, or to two HQCN and two methanol
ligands, forming HQCN2(MeOH)2M. Thereafter, the later complex catalyzes the conversion of
HQCN to the imidate HQOMe, while becoming unstable. The new imidate ligand replaces the
two acetate molecules, resulting in the heteroleptic complex as the kinetic product. The
complexes Terpy2M and (HQOMe)2M might also be generated but the equilibrium is shifted
towards the heteroleptic TQ’M product because of its low solubility in methanol, which allows
for its rapid precipitation out of the solution. Dissolving TQ’M in acetonitrile and heating it for
several hours prevent its rapid precipitation thus shifting the equilibrium back towards the
formation of the homoleptic complexes Terpy2M and (HQOMe)2M, leading to their formation as
the thermodynamic products that exist in the solution with TQ’M.
This mechanism emphasizes the role of the solvent in the formation of the heteroleptic
complexes. Considering these results, we propose a new approach for the formation of
heteronuclear complexes via a solventꢀbased synthetic control. In order to support our suggested
approach, we wished to investigate whether we can prepare TQ’Co directly from Terpy,
HQOMe and cobalt acetate. To this aim, we have synthesized HQOMe, based on a previously
reported procedure (see experimental section) and it with equimolar solution of Co(acetate)2 and
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Terpy, in the same reaction conditions as we have used above. The obtained complex was
analyzed by UVꢀVis and ESIꢀMS, exhibiting spectra identical to the ones acquired from the
analysis of the complex synthesized from HQCN (Fig. S5 and S22). The complex was reꢀ
dissolved in acetonitrile and crystalized by slow diffusion of diethyl ether to this solution. We
could see that the cell parameters obtained from the Xꢀray analysis of this product were identical
to ones obtained for TQ’Co complex. Thus, we demonstrated that this complex could be
obtained independently as an evidence for the synthetic control we propose in the introduction.
Finally, we wished to investigate whether a reaction of Cu2+ with Terpy and HQCN in
methanol will also lead to the formation of the carboxyimidate ligand (HQOMe) and to a
hexacoordinated copper complex. To this aim, we attempted to synthesize the complex using the
same reaction conditions applied in the synthesis of TQCu (see above) but with methanol as a
solvent instead of acetonitrile. The product was precipitated after addition of aqueous solution of
NH4PF6, washed and dried. The MS analysis of the complex showed a peak at 497
corresponding to the calculated mass of the expected complex TQ’Cu (Fig. S37). Due to its poor
solubility in methanol, this complex was further reꢀdissolved in acetonitrile and crystalized by
diffusion of diethyl ether into its solution. Interestingly, the Xꢀray structure of the complex
revealed a dinuclear Cu(II) complex T2Q’Cu2, in which one copper ion is hexaꢀcoordinated
through a Terpy ligand and a HQCN ligand, which was indeed converted to carboxyimidate
forming the HQOMe ligand, and another copper ion is pentaꢀcoordinated by the HQOMe ligand
through oxo bridge to another Terpy ligand and to one acetonitrile molecule (Fig. 4). We
therefore suggest that upon reꢀdissolving the complex in acetonitrile, a solvent molecule
coordinates to a tetraꢀcoordinated copper ion leading to a diꢀcopper complex, which crystallizes
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from the solution. This complex represents the ability of Cu2+ to adopt both a hexaꢀcoordination
as well as a pentaꢀcoordination, which is not apparent in the case of Co2+ and Ni2+.
Fig. 4 Xꢀray and a Chemdraw structure of T2Q’Cu2 complex that was synthesized in MeOH.
Color code: C, gray; N, blue; O, red; Cu, green. Hydrogen atoms omitted for clarity. Ellipsoids
are drawn at 50% probability level.
Overall, the structural data support our previous conclusions regarding the selective binding
of Cu2+ ion from the mixture of other metal ions.10 Both Co2+ and Ni2+ promote a reaction that
will enable them to coordinate to six atoms towards the formation of octahedral geometries, as
they are unable to form stable pentaꢀcoordinated complexes. The selectivity to Cu2+, which we
previously reported10 can now be rationalized as a consequence of specific intramolecular
binding to both HQ and Terpy via the formation of square pyramid geometry, a structure that
could be stabilized by Cu2+ but not by Co2+ or Ni2+.
Formation of Q’4Q’’2Mn4 cluster. Applying the synthetic procedure that yielded the
heteroleptic complexes TQ’Co and TQ’Ni to a reaction between an equimolar solution of Terpy
and HQCN in methanol and Mn(acetate)2, a yellow powder was obtained after precipitation with
aqueous solution of NH4PF6. This was recrystallized by vapor diffusion of diethyl ether into its
acetonitrile solution. The Xꢀray analysis revealed a cluster comprising of four Mn2+ ions
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coordinating six HQ ligands, which was crystallized in the monoclinic crystal system (Fig. 5A).
According to the Xꢀray structure determination, two types of binding environments about the
Mn2+ ions were observed: four triꢀdentate HQOMe ligands with coordinative imidate and two biꢀ
dentate HQO2Me ligands, in which the carbonitrile groups had converted to form methyl ester
groups that do not participate in the metal binding (Fig. 5A). Based on the definition of
heteroleptic complexes, which specify them as complexes composed of metal ion(s) coordinating
two different types of chelators,5 Q’4Q’’2Mn4 can be also considered a heteroleptic complex.
This cluster contains a [Mn4II (µ3ꢀO)2(µ2ꢀO)4N10]2+ core and each Mn ion has six coordination
arrangements with octahedral geometry displaying JahnꢀTeller axial elongation distortion. The
metal oxidation state of each Mn atom was established to be +2 based on charge considerations:
the inner Mn(2) and Mn(3) ions coordinate two nitrogen atoms and four oxygen atoms, and the
outer Mn(1) and Mn(4) ions coordinate three nitrogen and three oxygen atoms with overall four
bridging oxygens (O4, O5, O10 and O11) and two tripleꢀbridging oxygens (O7, O8) (Fig. 5B).
The distances between the HQ pairs that coordinate in an alternative manner are in the range of
3.3ꢀ3.8Å, which is in agreement with πꢀπ stacking interactions16 that the HQ aromatic rings can
be involved in. UVꢀVis analysis of this complex revealed absorption bands near λ = 257 and 283
nm originated from the two different types of HQ residues (Fig. S11). The mass of the cluster
was confirmed by APCIꢀMS analysis (Fig. S38). Attempts to synthesize the heteroleptic complex
TQ’Mn by addition of a mixture solution of Terpy and HQCN to a solution of Mn(acetate)2 in
acetonitrile yielded a yellow precipitate. This was crystallized by vapor diffusion of diethyl ether
to its methanolic solution. Similar to the results with cobalt acetate in acetonitrile, the Xꢀray
structure was consistent with the formation of the mono(terpyridine)manganese(II)bis(acetate),
TMn (Fig. S44). Other attempts to synthesize the TQMn complex including varying the ratio
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between HQCN and Terpy, changing the order of ligand addition and modifying the ratio
between HQCN and Terpy yielded a mixture of products with the major products being TMn
and T2Mn; the formation of T2Mn was realized from UVꢀVis and ESIꢀMS (Fig. S13 and S25).
Fig. 5 Xꢀray structure of (A) Q’4Q’’2Mn4 cluster and (B) its coordination core. Color code: C,
gray; N, blue; O, red; Mn, purple. Hydrogen atoms omitted for clarity. Ellipsoids are drawn at
50% probability level.
Moreover, aiming to synthesize Q’4Q’’2Mn4 independently, we have used the commercially
available 8ꢀhydroxyꢀ2ꢀquinolinecarboxylic acid in order to prepare HQO2Me by a simple
esterification reaction (see experimental section). This was further reacted in a mixture with
HQOMe and Mn(acetate)2 using an appropriate ratio between all the reactants at the same
reaction conditions in which this cluster was previously obtained. The product was analyzed by
UVꢀVis exhibiting a spectrum, which was different from the UVꢀVis spectrum of Q’4Q’’2Mn4
(Fig. S12) suggesting that the complex that was obtained in this method is different from the
Q’4Q’’2Mn4 cluster. The new complex was crystallized by diffusion of diethyl ether to a
complex dissolved in acetonitrile but to date, highꢀresolution structure by Xꢀray analysis could
not be obtained, however the analysis exhibits cell parameters different form the Q’4Q’’2Mn4
parameters, supporting the assumption that different complex was obtained. Attempts to change
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the ratio of the reactants and the reaction time yielded the same UVꢀVis spectrum, which is
different that this of Q’4Q’’2Mn4. Nevertheless, we believe that the mechanism for the formation
of Q’4Q’’2Mn4, which probably involves selfꢀassembly in solution, is more complicated that the
formation mechanism of the TQ’M complexes. Therefore, even though we cannot obtain this
cluster directly from the two HQOMe and HQO2Me ligands, we cannot exclude in this case the
synthetic solvent control we propose in the introduction.
Cyclic Voltammetry (CV) of the complexes. The heteroleptic complexes obtained in this
study were analyzed by cyclic voltammetry and their redox properties were realized (Fig. 6). The
heteroleptic copper complex TQCu undergoes a quasiꢀreversible oxidation of Cu2+/3+ at an Ep =
0.76V vs. Ag/AgNO3 and irreversible reduction peak of Cu2+/+ at Ep = ꢀ0.2V. The oxidation peak
at 1.04V may be attributed to the ligandꢀcentered irreversible oxidation processes (Fig. 6A).
Differential Pulse Voltammetry (DPV) analysis revealed an oxidation process of Cu2+/3+ centered
at 0.8V followed by oxidation of the ligand at 1.0 V (Fig. S46). The heteroleptic cobalt complex
TQ’Co exhibits reversible oxidation of Co2+/3+ coupled at Ep of 0.04V (Fig. 6B). The cyclic
ox
voltammogram (CV) of the heteroleptic TQ’Ni complex exhibits a quasiꢀreversible peak
centered at Ep = 0.58V, which corresponds to Ni2+/3+ oxidation potential followed by irreversible
reduction of Ni2+/+ couple at Ep = ꢀ0.82V (Fig. 6C). The DPV analysis of this complex show one
oxidation peak at 0.48V associated to Ni2+/3+ oxidation process (Fig. S47). The CV of
Q’4Q’’2Mn4 suggests irreversible two oxidation processes of the Mn ions from the oxidation
state +2 to +4. According to the Xꢀray analysis there are two types of Mn atoms, the inner atoms
coordinate to four oxygen atoms and two nitrogens while the outer Mn ions coordinate to three
oxygens and three nitrogens. Therefore, we would expect to see distinct oxidation potentials of
each type of Mn ion, with the Mn ions connected to four oxygen atoms displaying higher
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oxidation potential due to larger electronegativity of the oxygen atoms that withdrawing electron
density from the metal center. Indeed, the CV of the complex displays one oxidation peak around
0.76V, which may be attributed to Mn2+/3+ oxidation processes of two different types of Mn ions
that overlap, followed by further two oxidation processes of Mn3+/4+ at 1.08V and at 1.48V. DPV
analysis (Fig. S48) reveals three oxidation peaks centered at 0.7V, 1.02V and 1.34V with the first
peak being relatively wide, supporting our assumption of two overlapping signals assigned to the
Mn2+/3+ oxidation of two different types of Mn atoms.
Fig. 6 Cyclic voltammograms of metal complexes (A) TQCu (1 mM), (B) TQ’Co (1 mM), (C)
TQ’Ni (1 mM) and (D) Q’4Q’’2Mn4 (0.5 mM) that were recorded in acetonitrile at rt. with 0.1
M TBAꢀPF6 as the supporting electrolyte using glassy carbon working electrode, platinum
counter electrode, Ag/AgNO3 reference electrode. Scan rate: 100 mV sꢀ1.
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Conclusions
In this work we describe the synthesis of unique heteroleptic complexes based on 8ꢀhydroxyꢀ
2ꢀquinolinecarbonitrile and Terpyridine ligands with the metal ions Cu2+, Co2+, Ni2+ and Mn2+.
This includes full characterization by Xꢀray diffraction, EPR, UVꢀVis, HRꢀESIꢀMS,
paramagnetic NMR, elemental analysis, DFT calculations and cyclic voltammetry. Our results
demonstrate the effect of the solvent used during the synthesis on the nature of the complexes
formed. In acetonitrile we could only obtain the heteroleptic complex TQCu that has a pseudo
square pyramidal geometry. Using similar reaction conditions in methanol we could generate
heteroleptic complexes of Co2+, Ni2+ and Mn2+ due to methanolysis of carbonitrile to
carboxyimidate, which resulted in additional coordination site to form octahedral complexes.
These findings support our previous hypothesis regarding the association between the high
affinity and selectivity of a Terpy(HQ)peptidomimetic oligomer to Cu2+ over Co2+, Ni2+, and
Mn2+ and provide insights into the coordination geometry of the formed metallopeptoid
complexes. Importantly, this study emphasizes the challenges in the synthesis of heteroleptic
complexes suggesting an additional path for their production, which considers the solubility
properties of the homoleptic products. Moreover, our results suggest that the use of different
solvents, especially ones that can coordinate metal ions and/or react with the other ligand(s), can
assist in obtaining heteroleptic complexes not only as a result of solubility changes but also due
to ligand(s) modification. This observation should be applicable for numerous ligand systems
towards the construction of various heteroleptic complexes, clusters and biomimetic chelators.
Experimental section
Materials. Ammonium hexafluorophosphate, 2,2’:6’,2’’ꢀTerpyridine, sodium methoxide and
nickel acetate tetrahydrate were purchased from Alfa Aesar; 8ꢀhydroxyꢀ2ꢀquinolinecarbonitrile,
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and manganese acetate tetrahydrate were purchased from Acros; cobalt acetate tetrahydrate and
copper acetate monohydrate were purchased from MERCK; tetrabutylammonium
hexafluorophosphate (TBAP) was purchased from Fluka; copper(II) trifluoromethanesulfonate,
acetonitrile (ACN) and 8ꢀhydroxyquinoline were purchased from SigmaꢀAldrich; methanol
(MeOH) was purchased from Macron, 8ꢀhydroxyꢀ2ꢀquinolinecarboxylic acid was purchased
from Maybridge. These reagents and solvents were used without additional purification.
Methods. Mass spectrometry measurements were performed on a Advion expression CMS
mass spectrometer under electrospray ionization (ESI), direct probe with ACN (0.1% formic
acid), flow rate 0.2 ml/min, on Brucker maxis II mass spectrometer under atomic pressure
chemical ionization (APCI) or under electrospray ionization (ESI) and on Waters LCT Premier
mass spectrometer under electrospray ionization (ESI), direct probe ACN:H2O (70:30), flow rate
0.3 ml/min. UVꢀVis measurements were performed using an Agilent Cary 60 UVꢀVis
spectrophotometer. Electrochemistry was carried out on Iviumstat XRe potentiostat. EPR spectra
were recorded on a Bruker EMXꢀ10/12 Xꢀband (ν=9.4 GHz) digital EPR Spectrometer, in frozen
ACN solution at 150K temperature with (2,2,6,6ꢀTetramethylꢀ1ꢀpiperidinyl)oxidanyl (TEMPO,
g=2.0059) in an inner tube for determination of the gꢀfactor. Spectra processing and simulation
were performed with Bruker WINꢀEPR and SimFonia Software. For the Xꢀray crystallographic
measurements single crystals were absorb in Paratone–N oil and mounted on a Kappa CCD
diffractometer under flow of liquid nitrogen, except of TQCu, which was measured at 293K.
Data collection was performed using monochromated Mo Kα radiation (λ = 0.71073 Å) using φ
and ω scans to cover the Ewald sphere.17 The structures were solved by SHELXSꢀ97 direct
methods and refined by the SHELXLꢀ97 program package.18 The atoms were refined
anisotropically and hydrogen atoms were included using the riding model. Mercury 3.5 Software
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was used for the graphic representations.19 The calculations were performed with the Gaussian
09’ software, using the PBE1PBE functional with the 6ꢀ31+G(d,p) basis set. Stable=opt utility
was employed to ensure the conversion of the wavefunction to the lowest state. All geometries
were optimized ensuring a local minimum configuration with all positive frequencies. Elemental
1
analyses were performed on a Flash 2000 Thermo Scientific Organic Elemental Analyzer. Hꢀ
NMR and 13CꢀNMR measurements were performed on Bruker spectrometers AVIII400 and
AVIII500.
Synthesis of the heteroleptic complexes.
General. To a solution of metal ions (0.215 mmol, 43mM) in 5 mL ACN or MeOH an equimolar
amount of the ligands Terpy and HQCN (50 mg and 36.5 mg respectively, 0.215 mmol, 43mM
each) in 5 mL ACN or MeOH was added dropwise. After stirring for 2 hours at 50°C the
complexes were precipitated by addition of 10 folds excess of NH4PF6 in 10ꢀ20 ml of water. The
precipitates were separated from the solution by centrifugation, washed twice with water and
lyophilized overnight. To obtain single crystals for Xꢀray analysis the complex TQCu was
crystalized by slow evaporation from an ACN/THF solution. Other complexes were crystalized
by vapor diffusion of diethyl ether to their ACN solution.
TQCu: To a solution of 1 equiv. of Cu(II) triflate (77.7 mg, 0.215mmol, 43mM) in 5 mL ACN
an equimolar amount of the ligands Terpy and HQCN was added. Final product weight and
yield: 78 mg, 60%. HRꢀESIꢀMS: calculated [M]+: 465.0645; found: 465.0645. UVꢀVis: λ = 266,
325 and 338 nm. Elemental analysis for the precipitate: (C25H16N5OCuPF6) calculated: C:
49.15%, H: 2.64%, N: 11.46%; found: C: 49.94%, H: 2.92%, N: 11.46%.
TQ’Co: To a solution of 1 equiv. of Co(II) acetate (53.5 mg, 0.215mmol, 43mM) in 5 mL
MeOH an equimolar amount of the ligands Terpy and HQCN was added. Final product weight
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and yield: 113 mg, 83%. HRꢀESIꢀMS: calculated [M]+: 493.0949; found: 493.0991. UVꢀVis: λ =
280 and 319 nm. Elemental analysis for the precipitate: (C26H20N5O2CoPF6) calculated: C:
1
48.92%, H: 3.16%, N: 10.97%; found20: C: 45.70%, H: 2.95%, N: 9.85%. H NMR (500 MHz,
CD3CN) Sharp peaks that span over almost 120 ppm.
TQ’Ni: To a solution of 1 equiv. of Ni(II) acetate (53.3 mg, 0.215mmol, 43mM) in 5 mL MeOH
an equimolar amount of the ligands Terpy and HQCN was added. Final product weight and
yield: 127 mg, 93%. HRꢀESIꢀMS: calculated [M]+: 492.0970; found: 492.0943. UVꢀVis: λ =
279, 320 and 334 nm. Elemental analysis for the precipitate: (C26H20N5O2NiPF6) calculated: C:
1
48.94%, H: 3.16%, N: 10.97%; found20: C: 45.37%, H: 3.11%, N: 9.96%. H NMR (500 MHz,
CD3CN) Sharp peaks that span over almost 100 ppm.
Q’4Q’’2Mn4: To a solution of 1 equiv. of Mn(II) acetate (52.5 mg, 0.215mmol, 43mM) in 5 mL
MeOH an equimolar amount of the ligands Terpy and HQCN was added. After precipitation, the
complex was recrystallized from the ACN/ether solution. Final product weight and yield: 82 mg,
66%. APCIꢀMS: calculated [M]+: 1424.09; found: 1423. 43. UVꢀVis: λ = 257 and 283 nm.
Elemental analysis for the precipitate: (C66H48N10O14Mn4P2F12) calculated: C: 46.32%, H:
2.82%, N: 8.17%; found20: C: 42.71%, H: 2.93%, N: 9.37%.
T2Q’Cu: To a solution of 1 equiv. of Ni(II) acetate (42.8 mg, 0.215mmol, 43mM) in 5 mL
MeOH an equimolar amount of the ligands Terpy and HQCN was added. Final product weight
and yield: 115 mg, 84%. UVꢀVis: λ = 273, 326 and 339 nm.
Synthesis of methyl 8-hydroxyquinoline-2-carboxyimidate (HQOMe). Methyl 8ꢀ
hydroxyquinolineꢀ2ꢀcarboxyimidate was synthesized similarly to a previously published
procedure.21 To the solution of 8ꢀhydroxyꢀ2ꢀquinolinecarbonitrile (0.5 g, 2.94 mmol) in
methanol (20 ml) MeONa was added (50 mg, 0.926 mmol) and the mixture was stirred for 24
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hours at 40°C. The solution was dried by vacuum and the product was dissolved in ethyl acetate
(30 ml), washed by water and brine, dried over MgSO4 and the solvent was evaporated to give a
final product as a paleꢀyellow solid (0.52 gr, 88% yield). 1H NMR (400 MHz, CDCl3) δ 4.02 (s,
3H), 7.16 (d, J=7.6Hz, 1H), 7.31 (d, J=8.4Hz, 1H), 7.44 (t, 1H), 7.91 (d, J=8.5 Hz, 1H), 8.2 (d,
J=8.5Hz, 1H). 13C NMR (100 MHz, CDCl3) δ 54.26, 111.04, 117.89, 119.03, 129.25, 137.44,
137.88, 145.51, 152.47, 166.61. ESIꢀMS: calculated [M+H]+: 203.22; found: 203.11.
Synthesis of methyl 8-hydroxyquinoline-2-carboxylate (HQO2Me). Methyl 8ꢀ
hydroxyquinolineꢀ2ꢀcarboxylate was synthesized similarly to a previously published procedure.22
To the solution of 8ꢀhydroxyꢀ2ꢀquinolinecarboxylic acid (0.3 gr, 1.59 mmol) in MeOH (10 ml)
four drops of concentrated sulfuric acid were added and the mixture was refluxed for 24 hours.
The solution was concentered by vacuum and saturated aqueous NaHCO3 was added to the
residue, the product was extracted with CH2Cl2, dried over MgSO4 and the solvent was
1
evaporated to give a final product as a yellow solid (0.24 gr, 73 % yield). H NMR (400 MHz,
CDCl3) δ 3.98 (s, 3H), 7.16 (d, J=7.7 Hz, 1H), 7.30 (d, J=8.3 Hz, 1H), 7.49 (t, 1H), 8.09 (d, J=8.4
Hz, 1H), 8.2 (d, J=8.6 Hz, 1H), 8.38 (s, 1H). 13C NMR (100 MHz, CDCl3) δ 52.96, 111.07,
117.69, 121.65, 129.75, 130.29, 137.28, 137.77, 145.40, 153.26, 165.53. ESIꢀMS: calculated:
203.06; found: 226.18 [M+Na]+.
Corresponding Author
* Eꢀmail: gm92@tx.technion.ac.il
Conflicts of Interest
There are no conflicts to declare.
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Acknowledgments
The authors thank Dr. Boris Tumanskii for his assistance with the EPR measurements and Mrs.
Larisa Panz for her assistance with the MS measurements.
Notes and references
1 A. S. Polo, M. K. Itokazu and N. Y. Murakami Iha, Coord. Chem. Rev., 2004, 248, 1343ꢀ1361.
2 (a) M. Schmittel and K. Mahata, Inorg. Chem., 2009, 48, 822ꢀ824; (b) M. L. Saha and M.
Schmittel, Inorg. Chem., 2016, 55, 12366−12375.
3 (a) M. Schmittel and V. Kalsani, Top. Curr. Chem., 2005, 245, 1ꢀ53; (b) S. De, K. Mahata and
M. Schmittel, Chem. Soc. Rev., 2010, 39, 1555ꢀ1575.
4 M. L. Saha, S. Neogi and M.Schmittel, Dalton Trans., 2014, 43, 3815–3834.
5 M. L. Saha, S. De, S. Pramanik and M. Schmittel, Chem. Soc. Rev., 2013, 42, 6860ꢀ6909.
6
J. Frey, C. Tock, J. P. Collin, V. Heitz, J. P. Sauvage and K. Rissanen, J. Am. Chem. Soc.,
2008, 130, 11013ꢀ11022.
7 (a) M. Schmittel, B. He, J. Fan, J. W. Bats, M. Engeser, M. Schlosser and H.ꢀJ. Deiseroth,
Inorg. Chem., 2009, 48, 8192ꢀ8200; (b) S. Neogi, G. Schnakenburg, Y. Lorenz, M. Engeser and
M. Schmittel, Inorg. Chem., 2012, 51, 10832ꢀ10841; (c) S. Neogi, Y. Lorenz, M. Engeser, D.
Samanta and M. Schmittel, Inorg. Chem., 2013, 52, 6975ꢀ6984.
8 (a) W. M. Bloch, Y. Abe, J. J. Holstein, C. M. Wandtke, B. Dittrich and G. H. Clever, J. Am.
Chem. Soc. 2016, 138, 13750 –13755; (b) W. M. Bloch, J. J. Holstein, W. Hiller and G. H
Clever, Angew. Chem. Int. Ed., 2017, 56, 8285 –8289.
9 (a) V. C. M. Smith and J.ꢀM. Lehn, Chem. Commun., 1996, 2733ꢀ2734; (b) B. Hasenknopf, J.ꢀ
M. Lehn, G. Baum and D. Fenske, Proc. Natl. Acad. Sci., 1996, 93, 1397ꢀ1400; (c) D. P.
Funeriu, K. Rissanen and J. M. Lehn, Proc. Natl. Acad. Sci., 2001, 98, 10546–10551; (d) A.ꢀJ.
Zhang, C.ꢀJ. Chen, D.ꢀY. Lou, Y.ꢀH. Miao, C.ꢀX. Qiao and J.ꢀB. Hu, Z. Anorg. Allg. Chem.
2016, 642, 817ꢀ822.
10 M. Baskin and G. Maayan, Chem. Sci., 2016, 7, 2809ꢀ2820.
23

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11
(a) S. F. Sousa, A. B. Lopes, P. A. Fernandes and M. J. Ramos, Dalton Trans., 2009,
7946−7956; (b) C. Andreini, I. Bertini and G. Cavallaro, PLoS One, 2011, 6, e26325; (c) A. M.
Goforth, M. A. Tershansy, M. D. Smith, L. Peterson, Jr. J. G. Kelley, W. J. I. DeBenedetti and
H. C. zur Loye, J. Am. Chem. Soc., 2011, 133, 603–612; (d) N. Elgrishi, M. B. Chambers, V.
Artero and M. Fontecave, Phys. Chem. Chem. Phys., 2014, 16, 13635ꢀ13644; (e) L. Mishra, K.
Bindu and S. Bhattacharya, Spectrochimica Acta Part A, 2005, 61, 807–813.
12 M. Zastrow and V. L. Pecoraro, Coord. Chem. Rev., 2013, 257, 2565ꢀ2588.
13 A. W. Addison and T. N. Rao, J. Chem. Soc. Dalton Ttrans., 1984, 1349ꢀ1356.
14 (a) J. Peisach, and W.E. Blumberg, Arch. Biochem. Biophys., 1974, 165, 691ꢀ708; (b) N. Wei,
N. N. Murthy and K. D. Karlin, Inorg. Chem., 1994, 33, 6093ꢀ6100; (c) B. Lucches, K. S.
Humphreys, D.ꢀH. Lee, C.D. Incarvito, R.D. Sommer, A. L. Rheingold and K. D. Karlin, Inorg,
Chem., 2004, 43, 5987ꢀ5998.
15 (a) P. F. B. Barnard, J. Chem. Soc. A., 1969, 2140-2144 ; (b) M. Jamnický, P. Segl'a and M.
Koman, Polyhedron, 1995, 14, 1837ꢀ1847; (c) V. Y. Kukushkin and A. J. L. Pombeiro, Chem.
Rev., 2002, 102, 1771−1802
16 C. A. Hunter and J. K. M. Sanders, J. Am. Chem. Soc., 1990, 112, 5525ꢀ5534.
17 Kappa CCD Server Software, Nonius BV, Delft, The Netherlands, 1997.
18 (a) G. M. Sheldrick, Phase annealing in SHELXꢀ90: direct methods for larger structures. Acta
Crystallogr., Sect. A: Fundam. Crystallogr., 1990, 46, 467ꢀ473. (b) ORTEP, TEXSAN Structure
Analysis Package, Molecular Structure Corp., The Woodlands, TX, 1999.
19 Mercury software CCDC: http://www.ccdc.cam.ac.uk/Solutions/CSDSystem/Pages/Mercury.
20
Low carbon in elemental analysis may be caused due to the presence of water in the
complexes. After the synthesis, the complexes are washed with water, therefore a hydrate form
of the complex can be formed. Elemental analysis based on the dihydrate form of the complexes:
(C26H20N5O2CoPF6·2H2O) calculated: C: 46.30%, H: 3.59%, N: 10.38%; found: C: 45.70%, H:
2.95%, N: 9.85%. (C26H20N5O2NiPF6·2H2O) calculated: C: 46.32%, H: 3.59%, N: 10.39%;
found: C: 45.37%, H: 3.11%, N: 9.96%. (C66H48N10O14Mn4P2F12·2H2O) calculated: C: 45.28%,
H: 2.99%, N: 8.00%; found16: C: 42.71%, H: 2.93%, N: 9.37%.
21 W. Zhang, P. Chen and G. Liu, Angew. Chem. Int. Ed., 2017, 56, 5336ꢀ5340.
22 K. G. Vaswani and M. D. Keranen, Inorg. Chem., 2009, 48, 5797ꢀ5800.
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